1. Field of the Invention
The present invention relates to a semiconductor device, a liquid crystal display device and a method of manufacturing a semiconductor device, and particularly relates to a semiconductor device and a liquid crystal display device, in which a contact portion in contact with an interconnection, an electrode or the like has a reduced contact resistance, as well as a method of manufacturing such a semiconductor device.
2. Description of the Background Art
Liquid crystal display devices of a thin film transistor type, which will be referred to as “TFT-LCDs” hereinafter, have been improved to achieve larger sizes and higher definition. In accordance with this, interconnections made of alloy, which is primarily formed of aluminum and has a relatively low resistance, have been employed for preventing signal delay on the interconnections such as a gate bus-line.
A method of manufacturing a TFT-LCD in the prior art will now be described by way of example with reference to the drawings. Referring to FIG. 20, an aluminum alloy film (not shown) of about 200 nm in thickness is formed on a surface of a glass substrate 102 by a sputtering method. A predetermined photoresist pattern (not shown) is formed on the aluminum alloy film.
Etching with etching liquid, which is primarily made of phosphoric acid, acetic acid and nitric acid, is effected on the aluminum alloy film masked with the photoresist pattern described above. Thereby, a gate electrode 104b including a gate bus-line as well as a common line 104c are formed in an image display portion A, and a terminal interconnection 104a (i.e., an interconnection 104a on the terminal side) is formed in a terminal portion B.
Referring to FIG. 21, a silicon nitride film 106 having a thickness of about 400 nm is formed by a CVD method of the like on glass substrate 102 so that terminal interconnection 104a, gate electrode 104b and common line 104c are covered with silicon nitride film 106. Then, an amorphous silicon film of about 200 nm in thickness is formed on silicon nitride film 106. Further, an n+-type amorphous silicon film of about 50 nm in thickness is formed.
A predetermined photoresist pattern (not shown) is formed on this n+-type amorphous silicon film. Anisotropic etching is effected on the n+-type amorphous silicon film and the amorphous silicon film masked with the photoresist pattern. Thereby, amorphous silicon films 107 and n+-type amorphous silicon films 108 each having an isolated form are formed.
Referring to FIG. 22, a chrome film (not shown) of about 400 nm in thickness is formed by a sputtering method or the like on silicon nitride film 106 so that amorphous silicon film 107 and n+-type amorphous silicon film 108 in the isolated form are covered with this chrome film. A predetermined photoresist pattern (not shown) is formed on the chrome film.
The chrome film thus masked with the photoresist pattern is etched to form drain electrodes 109a and source electrodes 109b. Thereafter, appropriate processing is performed to remove n+-type amorphous silicon film 108 located on each amorphous silicon film 108 which will form a channel region. Thereby, Thin Film Transistors (TFTs) T each including gate electrode 104b, drain electrode 109a and source electrode 109b are formed.
Referring to FIG. 23, a silicon nitride film 110 which covers and thereby protects thin film transistors T is formed, e.g., by the CVD method. A predetermined photoresist pattern (not shown) is formed on silicon nitride film 110.
Anisotropic etching is effected on silicon nitride films 110 and 106 thus masked with the photoresist pattern so that contact holes 111a are formed to expose the surfaces of drain electrodes 109a, respectively. Contact holes 111b are also formed for exposing the surfaces of terminal interconnections 104a, respectively.
Referring to FIG. 24, a transparent and conductive film made of oxide such as an ITO (Indium Tin Oxide) film of about 100 nm in thickness is formed on silicon nitride film 110 by the sputtering method or the like so that contact holes 111a and 111b may be filled with this ITO film or the like. A predetermined photoresist pattern (not shown) is formed on the ITO film.
The ITO film thus masked with the photoresist pattern is etched with etching liquid containing hydrochloric acid and nitric acid so that pixel electrodes 113a are formed in image display portion A, and terminal electrodes 113b are formed in terminal portion B. Each pixel electrode 113a is electrically connected to drain electrode 109a of thin film transistor T. Each terminal electrode 113b is electrically connected to terminal interconnection 104a. 
Then, a glass substrate and a color filter (both not shown) are disposed on the above structure with a sealing material (not shown) therebetween. Liquid crystal is supplied into a space between glass substrate 102 provided with thin film transistors T and the glass substrate covered with the color filter. Further, a drive IC (i.e., IC for driving) is mounted on a predetermined terminal portion. The TFT-LCD is completed through the manufacturing process described above.
In the TFT-LCD, as described above, alloy films primarily made of aluminum are used in the gate bus-lines including the gate electrodes, the terminal interconnections and others. The purpose of this is to prevent signal delays by employing the alloy primarily made of aluminum as materials of the electrodes and interconnections, and thereby reducing the resistances thereof.
In the conventional TFT-LCD, however, oxide aluminum is formed on the interface between terminal interconnection 104a and terminal electrode 113b particularly in the contact portion within contact hole 111b. Such oxide aluminum is probably formed, e.g., due to reaction, which occurs on the interface between terminal interconnection 104a made of the aluminum alloy and terminal electrode 113b made of the ITO film or another transparent and conductive oxide film, due to oxygen plasma processing after formation of the contact holes, or due to natural oxidization occurring as a result of exposure of the substrate to the atmosphere.
Since the oxide aluminum is formed in the contact portion as described above, a contact resistance may take on an extremely high value of 100 MΩ or more if the contact area is in a practical range. Therefore, good electric contact cannot be achieved between terminal electrode 113b and terminal interconnection 104a so that the TFT-LCD cannot operate appropriately.
Further, the etching liquid, which is used for forming pixel electrode 113a and terminal electrode 113b made of the ITO film, may spread into the structure through pinholes in silicon nitride films 110 and 106. Since the etching liquid contains hydrochloric acid and nitric acid as already described, terminal interconnection 104a and gate electrode 104b made of aluminum alloy may be etched or corroded.
For overcoming the above problems, therefore, such a structure is already proposed, e.g., in Japanese Patent Publication No. 7-113726 that a chrome film or the like is layered over the surfaces of terminal interconnection 104a and gate electrode 104b made of aluminum alloy. The chrome film thus layered provides good electric connection to the ITO film. Also, the chrome film has a sufficient resistance against chemical liquid, and therefore can protect the interconnections and others made of aluminum alloy.
For coating the surfaces of terminal interconnection 104a and gate electrode 104b made of aluminum alloy with another kind of metal film, however, a sputtering device must be provided with a metal target corresponding to such a metal film. For forming the interconnection and others, it is necessary to conduct different kinds of etching which correspond to the film qualities of the metal films, respectively. This increases the manufacturing cost, and also increases the number of manufacturing steps.